The ornamental design for an oblatespheroidlamp, as shown and described.
FIG. 1 is a side view of the oblate spheroid lamp taken from any direction.
FIG. 2 is a top view of the oblate spheroid lamp; and,
FIG. 3 is a bottom view of the oblate spheroid lamp.
Portions of the figures shown in broken line are not part of the claimed design. The oblate spheroid lamp is at least translucent to visible light through all design surfaces.